A patient using an artificial ventilator needs to undergo removal of sputum produced in the patient's trachea, by aspiration at periodic intervals. Such an operation for sputum is troublesome; this operation needs to be performed night and day; and nurses, caregivers, and others should bear a great burden of work.
In view of this, aspirating apparatuses that automatically perform the operation for sputum have been known. For example, sputum aspirating apparatuses for aspirating sputum of patients who have been artificially ventilated by tracheostomy are described in Patent Documents 1 and 2. These sputum aspirating apparatuses are configured to continuously produce negative pressure in order to aspirate sputum; and when the negative pressure of suction path becomes high, assume that the suction tube is blocked with sputum, and raise the negative pressure.    Patent Document 1: PCT International Publication No. WO2006/009283    Patent Document 2: Japanese Patent Application Laid-open No. 2007-117273